So far, about 8,200 mortgage holders who lost trackers through the actions of their lender have been identified by the banks, the Central Bank said.
But there are indications that this number is expected to rise well above 10,000 by the time the bank-wide probe ordered by regulators is completed in summer.
In an update on the tracker probe that 15 lenders have been told to carry out, Central Bank director of consumer protection Bernard Sheridan said lenders were at different stages in their investigations.
Banks were told last December to conduct investigations into their mortgage books, with large accountancy firms like KPMG and Deloitte advising a number of the institutions. The final results would then be reviewed by the Central Bank.
Mr Sheridan said all homeowners affected by the issue would be identified by the 15 lenders by the middle of 2017.
Thousands of homeowners who opted to fix their mortgages from 2006 onwards, when European Central Bank rates started rising, were then denied a return to their tracker when the fixed-rate period ended. Instead, they ended up paying high variable rates.
Now, when a customer is found to have lost a tracker through the wrongful actions of a lender, the lender has to stop charging the incorrect amount on the mortgage, review the account and assess the redress and compensation due.
"The Central Bank continues to challenge all lenders to ensure that they identify all impacted customers in a timely manner," Mr Sheridan said.
Tracker rates are a fraction of variable rates.
Financial adviser Pádraic Kissane, who specialises in tracker-restoration cases, said there was now an issue about the tracker interest rate affected customers were being put on.
Some people are getting back on trackers on rates of 3pc-plus, whereas most trackers are set at 1pc above the ECB rate.
Fianna Fáil's Michael McGrath said the taking of trackers from customers was a systematic practice. More than 50 people have been found so far who have lost their homes due to the tracker over-charging.
He called on the Central Bank to work out whether senior bankers had knowledge of the issue.
Bank of Ireland is the latest lender to admit taking trackers off customers who should not have lost them. The bank admitted to over-charging more than 4,000 customers.